Pentaerythritol manufacture



Sept. 30, 1952 c. w. GOULD 2,612,526

PENTAERYTI-IRITOL. MANUFACTURE Filed June 22, 1950 CONDENSINC HCHO AND CH3CHO IN THE PRESENCE OF' Ca(OH) AS CONDENSING AGENT BYSLOWLY ADIfiNG CI-I3CHO TO ggLEOrUS HCHO CONTAINING CONDENSING COMPLETING THE ADDITION OF CH CHO WHILE THE HCHO CONCENTRATION OF THE REACTION MIXTURE IS AT LEAST 0.8%

I- I TREATING THE REACTION MIXTURE WITH AN ACIDIC MATERIAL TO LOWER THE H I To AT MOST 9.0 I

PRECIPITATING THE CALCIUM IONS FROM THE REACTION MIXTURE AFTER THE C H CHO HAS BEEN COMPLETELY ADDED AND WHILE THE HCHO CONCENTRATION OF THE REACTION MIXTURE IS AT LEAST 08% TREATING THE REACTION MIXTURE WITH NaOH TO [REMOVING THE PRECIPITATED CALCIUM J REDUCE THE RESIDUAL HCHO CONCENTRATION VIA THE CANNIZZARO REACTION TREATING THE REACTION MIXTURE WITH NaoH TO REDUCE THE RESIDUAL HcHo EMO NG THE PRECIPITATED CONCENTRATION vIA THE CANNIZZARO CALCIUM REACTION 1 I TREATING THE REACTION MIXTURE WITH I AN ACIDIC MATERIAL T0 LOWER THE H I LTO 7.0-8.0 I

J RECOVERING PEN TAERYTHRITOL FROM A l-E lNvz -iOTUgiID. THE REACTION MIXTURE I I BY W AGENT.

Patented Sept. 30, 1952 HerculesPowder Company, Wilmington, a corporation of Delaware Application June 22, 1950, Serial No. 169,753

This invention relates to the manufacture of 'p'e'ntaerythritol. More particularly, it relates to a process for the manufacture of pentaerythritol using lime or Ca(OH)2 as condensing agent whereby there is obtained aproduct of exceptionally low phthalate ester color.

' -A very important characteristic of a pentaerythritol is its phthalate ester color. This is particularly' so when the pentaerythritol is to be employed as the polyhydric alcohol in the manu- 'facture of phthalate alkyd resins. Briefly described, the phthalate ester color of a pentaerytham has reference to the color of a V thickness of a phthalate ester of the. pentaerythritol prepared under standard conditions. The phthalate ester color of -a pentaerythritol is expressednumerically, and the numbers used refer to'an arbitrarily defined color scale. Spectrophotometric readings on numerous samples of pentaerythritol phthalate esters prepared under the standardconditions have indicated that the colors can be gradedon the :c-trichromatic scale,

basis of Illuminant C. Accordingly, this scale has been arbitrarily divided into equal intervals over the range of color likely to be encountered and these numbered to 10. A pentaerythritol having-a phthalate ester color of 0' is productive of a phthalate ester which is water-white in color, etc. This matter is discussed more fully hereinafter, and the standard test for determining phthalate ester color is set forth. I 1 Lime or calcium hydroxide is a well-known cat-' alyst or'con'densing agent for pentaerythritol manufacture. (The terms catalyst and condensing agen as used herein have the same meaning-and are used interchangeably.') It :poss'esses certain advantages over other .known condensing agents for formaldehyde andacetal For example, the use of lime as condeh'yde. densing agent generally results in somewhat higher yields of crystalline product as compared with theQ-us of caustic soda. The lime-condensed crystalline product also has on the average ti -somewhat higher pentaerythritol monomer content','i. e., the pentaerythritol monomer'content of'the crystalline product as determinedby dibe'nzal analysis is somewhat higher in the case of the. crystallineproduct obtained from a limecondensedzreactionp a I The above factors favor the use of lime as coniien'si-ng' agent'overcaustic soda. However, it hasbeenexceedingly difiicult, if not impossible, to obtain pentaerythritol havinga low phthalate ester color-on the basis of a lime-condensed reacition'. l?entacrythritols having phthalate ester 19 Claims. (Cl. 260-635) colors of the order of 5.5' to "7.5 are therule in the case of lime condensation. Such -'a pentaerythritol does not meet the color requirements which have been established for phthalate' alkyd resin manufacture. For many end uses phthalate alkyd resins prepared from such pentaerythritols have no practical utility. In other cases the utility of these resins is borderline. It is ob+ vious, therefore, that the poor phthalate ester color of lime-condensed pentaerythritols. represents a technical problem of some real significance to this art. i

One important feature of this invention relates to the condensation step of the overall process for making pentaerythritol. It has now been found that, in order to obtain a pentaerythritol of low phthalate ester color when .Ca.(OI-I).: is used as condensing agent, it is quiteimportant that the acetaldehyde be added to the formalde- 20 hyde in the form of an aqueous solution containing condensing agent in such a manner that the concentration of acetaldehyde in the'reaction mixture at no time builds up to an appreeciable value. This requirement is accomplished as by adding acetaldehyde continuouslyand slowly to formaldehyde in aqueous solution,;maintaining the formaldehyde concentration of the reaction mixtureduring the addition of acetaldehyde suflicently high to promote rapid reactionoithe acetaldehyde with the formaldehyde, andistopping the addition of a the acetaldehydeprior to the point where the formaldehyde remainingin the reaction mixture is so dilute that rapid'reaction of the acetaldehyde with formaldehyde is not possible. It has been determined experimentally that the minimum formaldehyde. concen- .tration .of the reaction. mixture which will pro:- vide reasonably rapid reaction of acetaldehyde with formaldehyde is about 0.8% by weight. Hence, it is important to maintain the formaldehyde concentration of the reaction'mixtureatlor above thisconcentration during the periodic! addition. of acetaldehyde and to stoptheiaddition of acetaldehyde at or above this-.concenia .tration. As a practical matter, to provide 'a factor of safety'in the reaction it isprefe'rred to carryout the process in such a .ma'nnenthat the formaldehyde concentration of" the: reaction mixture is maintained at or above 1.0% during the addition of acetaldehyde and the, addition of acetaldehyde is stopped at orabove thisl'min'i- .mum concentration. If at any time during the reaction a substantial quantity of acetaldehyde is allowed to build up in the reactionmixturaathe selfcondensation of acetaldehyde withitself cium ions from the reaction mixture, filtration of the precipitate from the reaction mixture, evaporation (preferably under vacuum) of the reac tion mixture and crystallization of the pentaerythritol from the reaction mixture.

To achieve a reactionmixture having a formaldehyde concentration of 0.8% or above, preferably 1.0% or above, at.the time all of the aceta'ldehyde has been added, onemay employ various expedients. One expedient is to use a molar ratio of formaldehyde to .acetaldehyde substantially higherith'an. the theoretical molar ratio of 4.0 required for the reaction in conjunction with an aqueous formaldehyde of the usual concentration used for. pentaerythritol production (20% or thereabouts). For example; use of formaldehyde and acetaldehyde in the molar ratio of 4.5'jin conjunction with 20% formaldehyde will provide a formaldehyde concentration of the reaction mixture after all the acetaldehyde has been added of wellover.1.0%. The; desired result may also be achieved by using formaldehyde to acetaldehyde ratios well below 4.5 by starting with an aqueous formaldehyde having a higher formaldehyde concentrationin the beginning. Furthermore, the reactionmixture may be fortified with formaldehyde toward the end of the reaction to maintain theformaldehyde concentration. of the reaction mixture above 0.8% during the entire period that acetaldehyde is being-added to the reactionmixture;

It is evident from what'has been .saidheretofore that it is not necessary to place all or substantially all of the formaldehyde in thereactor atthebeginning of the run. For example, 50% orceven less of the total formaldehyde may be usecl 'initially and theremainder added at: inter- *vals throughout the condensation step. In fact, it isonly required in so far'as this invention is concerned that the concentration of formaldehyde in the reaction mixture beabove0.8 which is the-minimum concentration at which reasonably rapid reactionwith acetaldehyde takes place,

during the period of addition of acetaldehyde. Hence, it is-possibleqto start out a given run with :only-a'smallproportion of the total formaldehyde in the reactor, the remainder of the formaldehyde being added at intervalsthroughout. the condensation step: Whenthe process is carriedout in Ithisway, more care must be exercised tomake certain that the formaldehyde concentration of -the =reaction mixture is always at or above the minimum for reasonably rapid reaction of the iacetaldehyde, as compared with a process in which substantially all of the formaldehyde is in .th'e-reactor in the beginning. It is for this reason ithatwthe preferred procedure of this .invention comprises slow addition of acetaldehydeto substantially all of the formaldehyde.

1' While the process described above-:provides'a -':pentaerythritol having a'very desirable phthalate :ester color, the process is impractical from several pointsbfview, In the first place, the relatively:

reaction mixture gives rise to formaldehyde fumes in the plant. Aside from being disagreeable to "the workers in the plant, these fumes present a health hazard. s 1;.

It has been further found that advantage may be taken of the above discovery and at the same time the disadvantages abovementioned avoided by proceeding as follows. The important steps in this second discovery are the removal of the calcium ions from the reaction mixture and the reduction of the formaldehyde concentration of the reaction mixture to a lower level bytreate ment with NaOI-I. 2

When solutions of formaldehyde are. heated to temperatures in therange of 50-75;Q.- withsumcient sodium hydroxide to raise the pH above the formaldehyde concentration is readily reduced to a few tenths of one. per cent bythe Cannizaaro reaction. If, however, calcium ions are present in an alkaline solution of formaldehyde similarly treated, another type of; reaction takes placebesides the cannizzaroreaction. This-second 1388,9- tion is the formation of sugarelilre formaldehyde poly ers w ich. in the e ence. if-ta um ons. are autocatalytic. Before. the formaldehyde can be reduced, to the desired leveL, the polymerization reaction overtakes the Cannizzaro, reaction, and a coloredreaction mixture results. These formalde hyde polymers also-contributeto high phthalate ester color in the resulting pentaerythritol. Since the calcium ion is apparently necessary for this undesired'reaction, it can be circumvented byremoving the calcium ion prior to destroying-the formaldehyde by the Cannizarro reaction. After reduction of the formaldehyde concentration, the reaction mixture "is worked up by theusual steps of evaporationv (preferably underxreduqed b11 1 sure) and crystallization to provide, a crystalline product.

The reduction of the formaldehyde concentration of the reaction mixture may- .be;efiected.;to any desired extent. In general, .the-greaterthe reduction of ,the formaldehyde content, the less one has to contend with a fume problem in the operation. Furthermore, the greater the reduction. in: formaldehyde concentration, the v reater the yield of crystalline productit is preferred that the formaldehyde concentration of there..- actionmixture be reduced to- 0.6%; orbelow.

, ,The salient advantage ofthe process of this invention is of course thatv th'eLpenta-erythritOI obtained is much improved with--;;respect to phthalate ester color as compared zwith-the, pen.- taerythritol which normally results from calciumcondensed reactions. Thus, it.;is. possible ,using the. principles underlying this invention ;to :-make p a r h t l a n ph alateester-c or of 2.0 to 3.5. Furthermore... crystalline pentaeerythritol is obtained in equally; as'high yield zas in the conventional limeecondensed .reactions. ,Also, the pentaerythritolmonomer content .offlthe crystalline product is at least as'highandinsome cases higher. as compared -,witha..products. of the conventional lime-condensed processes.

' sis-12,1526

aldehyde and acetaldehyde'v in the presence-of catOHJ- z as vbandensing agent by slowly adding acetaldehydef toformaldehyde in the. form of an aqueous solution containing condensing. agent,-

the formaldehyde concentration of the reaction mixture during the entire period of addition of acetaldehyde being at least 0.8% by weight, the aldehydes being employed in such proportions that at the time the acetaldehyde has been completely' added the formaldehyde concentration of the reaction mixture is at least 0.8% by weight. The addition of acetaldehyde is completed while the: formaldehyde concentration of the reaction mixture is at least 0.8% by weight. The next step involves precipitation of the calcium ions from the reaction mixture while the formaldehyde concentration of the reaction mixture is at least'0.8% 'by weight. Preferably, the resulting precipitate is removed at this point. Thereafter, the resulting calcium-free reaction mixture is treated with NaOH to reduce the residual formaldehydeconcentration via the Cannizzaro reaction. If the precipitated calcium ions were notv removed priorto the last step they are removed at this point. Finally, pentaerythritol is recovered from the reaction mixture.

The invention is also shown in its broad aspect in the attached drawing. The drawing is self-explanatory. As illustrated, there are two alternative courses to follow once the precipitae tion of the calcium ion from the reaction mixture has been effected. One of these alternatives is toremove the precipitated calcium ion and then treat the reaction mixture withNaOH to-reduce the formaldehyde concentration via the Cannizzaro reaction. The other alternative involves simply these steps in reverse order. The steps enclosed by broken lines are steps which are not necessar'y'to achieve an operable process but which are preferably employed. Thus, the step following the completion of addition of acetaldehyde which comprises treating the reaction mixture with an acidic material to lower the pI-I to at most 9.0 is an optional step. Similarly, the step following the formaldehyde reduction. step of treating the reaction mixture with an acidic material to lower the pH to 7.0-8.0 is optional.

. ,Considering for the present. the condensation step of the process, as stated previously there are various ways in whichthe aldehydes maybe brought in contact. The method of ad in the condensing agent is in general not particularly critical. However, since Cami-I): is consumed as a reactant in the process, there should always be an excess of Ca(OH)g in the reaction mixture over and above that which has been converted to calcium formate. The pH, of the reaction .mi' xtureis indicative of whether or not an excess of Ca(OH)2 is present. A pH of at least 10' is preferred. The preferred procedure for contacting the aldehydes is to slowly and continuously add the acetaldehyde to substantially all of the formaldehyde in the form of an aqueous solu: tion. When this procedure is employed, there are several ways in which the condensing agent may be introduced. One procedure, for example, is to slowly add the acetaldehyde to a preformed mixture, of allof the condensing agentand the aqueous formaldehyde in a reaction vessel. The preferred procedure, however, is to add' the acetaldehyde and the condensing agent slowly and concurrently to the aqueous formaldehyde ,in thereaction vessel. in this latter procedure the acetaldehyde and the condensing agent are added separately; to the aqueous formaldehyde. This preferred procedure affords excellent control. of reactionrcondition's andleads to'high yields :of crystalline product. V e

.As stated, the additionzofuacetaldehyde is completed. while .the formaldehyde concentration of thereaction mixture is at least 0.8% by; weight.

This means that there must be an excess, ofzformaldehyde, employed over ,and above the 4,. to... 1 molar ratio theoretically required, for. the'conver: sion of acetaldehyde and ,formaldehydewto pen,- taerythritol, Eromthe standpoint ofproviding a practical operatingprocess, there, should ,be

employed a molar ratio of at least l Prefer: ab y. heo ar ra io .shouidbe i 14 U duly high molar ratios of formaldehyde andacetw aldehyde are to be avoided, While the process 0; this invention is not inoperable on the ,basis of such high molarratios, of formaldehyde ,and acetaldehyde, the use thereofis wasteful- -of formaldehyde and hence uneconomic. The uSxof such high ratios further makes, it necessaryto destroy additional formaldehyde in the "later formaldehyde reduction step. Inconformitywith the desirability of not employing unduly high. formaldehyde to acetaldehyde molar ratios, it is desirable to carry out the condensation reac tion in such a manner that at the completion of addition of acetaldehyde thefformaldehyde eoncentrationof the reaction mixture is at least 0.8% but atthe same time: not unduly high. Thus, it is preferred that the formaldehyde cone centration of the reaction mixture atthi spoint be within the range of 1.7% to 0.8 While concentrations higher than 1.7% are in nofway inoperable, operation underi'fsu'ch conditions is to be avoided fo'rfthe reasons" above-mentioned.

As stated above, thecondensation reactiorids carried out in an aqueous medium. In the prior art the manufacture of 'pentaerythritolhas almost without exception been' carriedoutfin a'queous'medium. The proportions of water to the other ingredients have varied over a ra'the'r wide range. So far as this invention is concerned, any of the prior art proportions may be employed. cated, use of formaldehyde solutions'ofrelatively high concentration is one means-of achievinga reaction mixture having a formaldehyde con-- centration of at least 0.8% at thecsmpieuo qar the addition of acetaldehydeiwithout employing particularly high formaldehyde to acetaldehyde mol' ratios. It is preferred; however -that-the aqueous formaldehyde whichis employed in car-- rying out this invention bebnehaving mom: aldehyde concentration of from 15%" to 35%;

This niean's,-of course,- that' when, the preferred I procedure for'carrying-out the condensation i's employed, the aqueous formaldehyde solution' to which the condensing agent and the acetaldehyde :are added will have' a formaldehyde con-'- centration of from 15% to 35%." W1 .zThe condensing agent employed is Ca-(OHh. Actually, lime or Ca(OH)z maybe employed. The condensing agent may be added to thereaction. mixture. as .such or in. the forrrr'of-an aqueous slurry. The reaction of acetaldehyde and formaldehyde to yield pentaerythritol theoretically requires /2 mol of Ca(OI-I)2 per mm of acetaldehyde. It is thepracticein the art,

' however, to employ as much.as-l0% or: more in excess; of the-theoretical amount. Intthe-prac tice of thisinventionany' of the-proportions em played h r t forebe used.

In fact, as has been previously indi-.

' *Whileznot:.aentirely"necessary it:is:ofttimesjsde+ enable .to' lower the: pH f. .the;reaction1.mixture aiterztheadditioniof acetaldehyde' has'been'come pleted. 'At this point-there is substantially no free acetaldehyde in the reaction :mixture but there is free formaldehydepresent. Underhighly alkaline. conditions; both i self-condensation of 0.51%; Suificient-formiciacidgwasaaddeditoreduce the -iformaldehyde .and f Cannizzaro reaction of thewfor'maldehyde with itself can take place. The

former reaction is particularly undesirable as previously pointed out; By reducing the alkalinity of 'the-reaction"mixture these reactions are largely avoided." Reduction to'a pI-I of'9.0 or'below is satisfactoryand any acidic -material; such as formic' acid; adeticacid, etc.may-be used. This step of reducing the alkalinity is espeoia'lly useful in plant operations where the I reaction mixture mustj' b'e held for some time before precipitation of the calcium; If 1 the calciumis precipitated soon after-the 'com'pletion'of the condensation step,pH-reduction is not needed. 1

The agent for reducing the residual'formaldehyde =concentration of the reaction mixture is NaGHs The -NaOH destroys the formaldehyde by converting-it via the Cannizzaro reaction into methyl-'alcohol'and formic acid. Sodium hydroxide' is used'for this step of the'processfor reasonspreviouslyindicated and due to the fact that it effects a smooth disappearance. of-the formaldehyde and provides a controllable reac tion: The amount *ofNaOH required is ;neces sari-1y afunction offthe amount of formaldehyde tOfb'e destroyed. ;The temperature and time or treatment are also iactorswhich haveja bearing onthe amount ofNaOH needed. In general; a temperature of from about '50", C, to about '75? C. is preferred for this'step. The preferred reachon-period is from :about 30 min, to about 120 min.

-fThere follow-specific examples which are il-' lustrative of the invention broadlydescribed herein'above: All parts and percentages in this application are bywei'ght'unless otherwise in-v dictated:

"Epample 1 Six hundred seventy-five parts of a 20% .iormaldehyde-water solution (approximately 4.5 mols of-iormaldehyde) was added to a vessel equipped -vvith a cooling ,coil and stirrer. To the solution was added-200 parts ofag2,0% calcium hydroxide-.

wateryslurry (approximately 0.54 mol of calcium hydroxide), the temperature being maintained ataboutf C Forty four parts of liquid acetal-e dehyde iapproximatel lfl mol) was added to .the

formaldehyde-calcium, hydroxide mixture bee neath T the: surface thereof a .during ,a period i of .32

theepH. of they mixtureto vbetweendb!) 513116.850. 'Ihe-amixtureiwas then concentrated by GVEQQI'BI? tionzunder; reduced: pressureeandrcooled.toicrvsw .tallize out: thevpentaerythritol. Thedriedsprode uctjhadca: phthalateester color of 2.5;to;3-.0

t. l Example 2" :gsixihundredseventy-fiveparts of a "formaldehydeewaterrsolution (approximately 4.5: mols ofiformaldehydeywere added to a vessel equipped with .a cooling. coiliand stirrer. Two; hundred parts of a .20 calcium: hydroxide-water slurry (approximately 0.54 mol) and 44. parts;of :liquid acetaldehyde (approximately 111101) were added separately and simultaneously to'the vessel our-:- ingna period- 0f ,2 hours. The addition ratewas such that theconcentration .of i acetaldehydzin the. reaction mixture at no time built up-ito" an appreciable value. The maximum temperature during this condensation period was '50? C. When the addition 'of acetaldehyde was completed,v the formaldehyde aconcentrationxof the reactiontmix-i ture Was-.1.5.%. Thei pH of thereaction mixture was then reduced to 9.0'with formi'c acid. While hours at such -a ratehithat atno time'did: the

conoentrationj of theacetaldehyde in vthe-reaction-mixture build up to an appreciable value.

'1 hem8 Ximum temperturei during the: addition wasjflj C. vWhenrthe addition of the acetaldee hyde was complete, the formaldehydeconcentration'of thepreaction mixture'was 1.5%. The pH; ,ofithe reaction mixture was reduced'to 9.0 wit 7 formic acid. -While. the formaldehyde con- Qentrationu of, thevreaction mixture was still at 1.5% all the calcium present was precipitated as calci-unrcarbonate by the addition-of 57 parts iapproxim-ately;i0.54. mol) of sodium carbonate. The calcium carbonate-precipitate wasth'en' removedrby :filtration. To the afiltrate Wasadded 40:.;-Darts::o.:a sodiu'm hydroxide-water-solw tion :(approximately 0.5-.mol)- and the tempera theiformaldehyde concentrationaof the reaction mixture was .still..1.5 .the calcium was precipitatedias'calcium carbonate :bythe addition of'57 parts (approximately 0.54 mol) of sodium car-.- bonate; The calcium carbonate precipitate was removed by filtration. To the filtrate :was added 40 parts of :a 50%sodium hydroxide water solua tion (approximately 0.5 mol sodium hydroxide) and the temperature raised to C; After about 1%z --h011I-S, theformaldehyde concentrationhad been reduced'to 0.5% Formic acid wasthen added'to reduce the pHof the mixture to between '7.'0and"8.0. Finally the mixture-was concentrated by evaporation under reduced pressure-land cooled to crystallize out the pentaerythritol; The dried product hada phthala'te ester color of 2.5 3.01

Thefi'r'st step of the-process-herein described is referred to as condensing formaldehyde-and acetaldehyde inthe presence of acondensing agent'to yield pentaerythritol. As is well known in the art, the chemical reaction here involved is not just a simple condensation.---ln fact, there are two difierent reactions takin'g'pl-ace: (1) aldol condensation of the formaldehyde and acetaldehyde to yield trimethy1ol==acetaldehyde-and (2) reaction of the trimeth ylolacetaldehyde-with formaldehyde bywhat is known as the Cann-izz'aro reaction to provide pentaerythritol --and formic acid- (which in the presence of calcium ions form calciumformate). It will be under stood; therefore, that the term condensing and related terms are used herein in, a sense to im cludethe reactions involved making pentaerythritol from-acetaldehyde and formaldehyde andis not to be construed as limited to-what is strictly speaking a condensation reaction.

'The condensation step of the process may-*be conducted under 'such 'conditions with'respect-to temperature as have been employed heretofore in thepriorart: Due tothe fact that the reactions involved are exothermic; there will be some variation in the-temperature of the-reaction mix ture in any practical use of the invention. The temperature of the reaction mixture is best con trolled by using the technique previously described of slowlyadding the' Ca('OH)'2 and'the acetaldehydeseparately and concurrently to the ture raised to 65 0.1 Aftrfabbut1% i hours, the 73 aqueousformaldehydefin'the reaction vessel. For

best-results" it is preferred to carry out thereon -tion under such conditions that the; temperature is not over 5030. In'the examples thec'alcium'ions were precipitated by. use of NazCOs. In. general, any known-precipitating agent for calcium ions may be 'ie'mployed. Examples are NazCOs, H2804, 'Na2SO4, ..:H2C2O'4, 'Na2C2O4; etc. .Water-soluble carbonates such as NazCOssarevery effective.

f aWhen caustic soda is used to reduce the residual formaldehyde content; of the reactionmixture; the resultingreaction mixture is usually 'highly alkaline. It"--is preferred; to reduce the alkalinity by addition of an acidic material in suchamount that a pI-I'of 7.0 to 8.0 obtains. Suitable'materials are formic acid, acetic-acid; etc.

"After the reaction mixture has beentreated toreduce the residual formaldehydecontentzit 'is th'en in conditionto' be treated for recovery 'of pentaerythritol. Any of thexknown recovery procedures may be used for this purpose.

The salient advantage of this invention is that-v it provides pentaerythritol which is much" im.- provedwith respect to phthalate.ester-'coloras compared' with' the pentaerythritol which normallyresults from calcium-condensed reactions. As evidence'd by the examples, it isiquite possible by utilizing the principles underlying this ine 'v'ention to make pe'nta'erythritol having phthalate estercolors of the order of-2.5'to 3.5-. aAt'the same time crystalline pentaerythritol isobtained in the process of this invention in equally as high yield, basedon the acetaldehyde. asin the cone ventional lime-condensed reactions. Furthermore, the -pentaerythritol monomer content of the crystallinepentaerythritol is at least ashigh and in'some cases higher as compared with products of the conventional lime-condensed reactions' U '"Ihe'phthalate ester color test referred to hereinaboveconsists in reacting pentaerythritol with reagent grade phthalic anhydride and measuring the c'olo'rof a%" thi'cknessof the resulting ester. Spectrophotometric readings on numerous 'samples"of pentaerythritol-phthalate esters prepared by-the method outlined below'have indicated that the colors can be graded onth'eirv trichromati'c scalefbasis'of Illuminant C. Ac-

cordinglygthis scale has been arbitrarily divided into equali'ntervals' over the range of color likely to be" encountered, and these numbered from 0 liO10. -1

For'p'racticalapplication this color scale has been duplicated by the use of Lovibond glasses for visual comparison.

, Yellow Red 1 (Series 510) '(Series200) In taming out the test phthalicanhydride,

Merckis reagent grade, sublimed M. P. 129-131" C. or equivalent isnemployed. For making the thicknesses of the phthalate ester there are employed the standardsize rosin color molds. Ad-

just the temperature'of an oil bathfrom 220-225 "C."and maintain it within this range for the dura''- -tion 'of thetest 'with the aid ofa hot plateyelec- "trio heater or flame. Clamp a test Etube'i'n the heated oil bathsothatit is about 0.5 immersed in-theoil and add 29.5 g. of phthalic anhydride. Place a thermometer in the tube and .stir the anhydri'de gently until it becomes molten and is f j The term formaldehyde-i concentration heated to 218-220 C iAdd 7,510,135.g;:=of'-.zthe pentaerythritol tobe tested all at-once. e-StirZ the contentsiof .the test tube-with the-thermometer I until the temperature reaches 215". ,C. .-All0w,;the tube:- and contents -to remain in the; bath: for-Pa total of minutes from, the time; of addition of the pentaerythritoLiremove and pourintoa rosin colorimold which has previously been heated to 100-140? C. A11OW-th6m01d andcontents to" cool slowly to room f'temperature and-compare: the color; with thestandards reading to the nearest 0.5 grade. I

- used herein means the freeformaldehydei-com centration of the mixture or 'compositioninvolv'ed as determined by means of apolarograpnqw :1 What I claim-and desire. to-prote'ct bysLetters Patent'isz. r

1 1.; The process forr preparing? pentaerythritol which comprises. condensing formaldehydeziand acetaldehyd-e in the presence of :CatOH) zxas coni densing agent by slowly adding acetaldehydeitb substantially all of theformaldehyd'e whicli in the form o'f 'an'aqueous solution containing rco'n' densing agent; the aldehydes being employed in such proportions that atthe- 'time the 'acetalde hyde hasbeen completely 'added 'theformalde e hyde concentration of the' reaction mixture is at I least 0.8% by weight, completing' theaddition of ritol from the resulting reaction mixt'ii duced formaldehydecontent.

which comprises condensing form substantially all of the formaldehyde .whic

ac'etaldehyde while the formaldehyde concentra- Ytion of the reaction mixture is at least"0.8%-

weight, precipitating the calcium fronfi jtlie re *tion mixture ,after' the acetaldehyde as completely added and" While the formald'ehyde concentration of the reactionimiiitiire{islet"least 0.8% by weight, subjectingthefreaction miiitui e to-the following two treatments inany'hide i'i'i vai 'o'f'the precipitate and treatment of the formaldehyde concentration vie 11 reaction, and finally'recovering thelp'e' ae The o ess r r in Pen. ei b acetaldehyde' in the presence of; Cami-Di n en byslqw y a n li ce aldc I the form of an aqueous.solutibn containing on,-

densing agent, the aldehyde-s being. employed in such .p'roportions that at the .time the acetallde hyde has been completely addedLthe'Iorma e;-

hyde concentration of the reaction. mixtureis within the range of from 1.7% to0.8%= by veight,

completing the addition of acetaldehyde while i the formaldehyde concentration-of the reaction mixture is within the range of from;1 .7%-to.0.8% by. weight, precipitating the calcium-.from'the reactionmixture after the acetaldehydehas ibeen completely added v ar 1d---while the formaldehyde concentration of the-reaction mixture'is wi hin the range of from 1.7% to 0.8%,by/weight3removin the resulting precipitate,-treating theresulting calcium-free reaction'mixture with .-Na0H to reduce the residual formaldehyde;concentra tion via the Cannizzaro reaction, andrejcove ng the pentaerythritol from the resultingreact io mixture of reduced formaldehyde content-,

3. The process for,preparing pentacrythritol I which comprises condensing; formaldehydeiand substantially all the formaldehyde which is in the form of an aqueous solution containing condensing agent, the aldehydes being employed in such proportions that at the time the acetaldehyde has been completely added the formaldehyde concentration of the reaction mixture is within the range of from 1.7% to 0.8% by weight, the aqueous formaldehyde employed having a formaldehyde concentration in the range of from 15% to 35%, the temperature during said condensation step being not over 50 C., completing the addition of acetaldehyde while the formaldehyde concentration of the reaction mixture is within the range of from 1.7% to 0.8% by weight, precipitating the calcium from the reaction mixture after the acetaldehyde has been completely added and while the formaldehyde concentration of the reaction mixture is within the range of from 1.7% to 0.8% by weight, removing the resulting precipitate, treating the resulting calcium-free reaction mixture with NaOH to reduce the residual formaldehyde concentration via the Cannizzaro reaction, and recovering the pentaerythritol from the resulting reaction mixture of reduced formaldehyde content.

17. The process for preparing pentaerythritol which comprises condensing formaldehyde and acetaldehyde in the presence of Ca(OH)2 as condensing agent by slowly adding acetaldehyde to substantially all the formaldehyde which is in the form of an aqueous solution containing condensing agent, the aldehydes being employed in such proportions that at the time the acetaldehyde has been completely added the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, completing the addition of acetaldehyde while the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, precipitating the calcium from the reaction mixture after the acetaldehyde has been completely added and while the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, treating the resulting reaction mixture containing precipitated calcium with NaOH to reduce the residual formaldehyde concentration via the Cannizzaro reaction, removing the precipitated calcium, and recovering pentaerythritol from the resulting reaction mixture.

18. The process for preparing pentaerythritol which comprises condensing formaldehyde and acetaldehyde in the presence of Ca(OI-I)2 as condensing agent by slowly adding acetaldehyde to substantially all of the formaldehyde which is in the form of an aqueous solution containing condensing agent, the aldehydes being employed in such proportions that at the time the acetalde- 14 hyde has been completely added the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, completing the addition of acetaldehyde While the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, treating the reaction mixture with an acidic material to lower the pH to at most 9.0, precipitating the calcium from the reaction mixture after the acetaldehyde has been completely added and while the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, removing the resulting precipitate, treating the resulting calcium-free reaction mixture with NaOH to reduce the residual formaldehyde concentration via the Cannizzaro reaction, and recovering the pentaerythritol from the resulting reaction mixture of reduced formaldehyde content.

19. The process for preparing pentaerythritol which comprises condensing formaldehyde and acetaldehyde in the presence of Ca(OH)2 as condensing agent by slowly adding acetaldehyde to formaldehyde which is in the form of an aqueous solution containing condensing agent, the formaldehyde concentration of the reaction mixture during the entire period of addition of acetaldehyde being at least 0.8% by weight, the aldehydes being employed in such proportions that at the time the acetaldehyde has been completely added the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, completing the addition of acetaldehyde while the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, precipitating the calcium from the reaction mixture after the acetaldehyde has been completely added and while the formaldehyde concentration of the reaction mixture is at least 0.8% by weight, removing the resulting precipitate, treating the resulting calcium-free reaction mixture with NaOI-I to reduce the residual formaldehyde concentration via the Cannizzaro reaction, and recovering the pentaerythritol from the resulting reaction mixture of reduced formaldehyde content.

CHARLES W. GOULD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,011,589 Paterson Aug. 20, 1935 2,329,514 Cox Sept. 14, 1943 2,401,749 Burghardt June 11, 1946 

1. THE PROCESS FOR PREPARING PENTAERYTHRITOL WHICH COMPRISES CONDENSING FORMALDEHYDE AND ACETALDEHYDE IN THE PRESENCE OF CA(OH)2 AS CONDENSING AGENT BY SLOWLY ADDING ACETALDEHYDE TO SUBSTANTIALLY ALL OF THE FORMALDEHYDE WHICH IS IN THE FORM OF AN AQUEOUS SOLUTION CONTAINING CONDENSING AGENT, THE ALDEHYDES BEING EMPLOYED IN SUCH PROPORTIONS THAT AT THE TIME THE ACETALDEHYDE HAS BEEN COMPLETELY ADDED THE FORMALDEHYDE CONCENTRATION OF THE REACTION MIXTURE IS AT LEAST 0.8% BY WEIGHT, COMPLETING THE ADDITION OF ACETALDEHYDE WHILE THE FORMALDEHYDE CONCENTRATION OF THE REACTION MIXTURE IS AT LEAST 0.8% BY COMPLETELY ADDED AND WHILE THE FORMALDEHYDE CONCENTRATION OF THE REACTION MIXTURE IS AT LEAST 0.8% BY WEIGHT, SUBJECTING THE REACTION MIXTURE TO THE FOLLOWING TWO TREATMENTS IN ANY ORDER: REMOVAL OF THE PRECIPITATE AND TREATMENT OF THE REACTION MIXTURE WITH NAOH TO REDUCE THE RESIDUAL FORMALDEHYDE CONCENTRATION VIA THE CANNIZZARO REACTION, AND FINALLY RECOVERING THE PENTAERYTHRITOL FROM THE RESULTING REACTION MIXTURE OF REDUCED FORMALDEHYDE CONTENT. 